Windows Server 2008: specifying the default IP address when NIC has multiple addresses

With Server 2008 Service Pack 2 (not R2), or Vista SP2 and MS hotfix KB975808 there is a solution, although a bit clumsy. You would remove all the addresses you DON'T want as a source, then re-add each one at the command line using

Netsh int ipv4 add address <Interface Name> <ip address> skipassource=true

The hotfix enables the "Skip As Source" flag.

For a deeper dive on how different Windows versions select source IPs, see this TechNet blog post.

There isn't such as thing as a "Default IP" for a network interface; rather your systems routing table defines which logical interface should be used when communicating with other devices.

It sounds like what you'd like to do is configure a default route. This would cause all conversations initiated by this machine to be made from a specific IP.

Use route add to add a default gateway